Integrated circuits, also known as “ICs” or microchips, are miniaturized electronic circuits that are used in virtually every electronic device constructed today. ICs are constructed by layering various materials (conductors and insulators) by imaging, deposition, and/or etching processes onto a wafer, typically constructed from silicon. Devices of the IC are formed by front-end-of-line processing and back-end-of-line processing is used to form interconnect levels and passive devices in the interconnect levels.
Die cut from the wafer are commonly mounted on a package carrier (such as a substrate, a circuit board, or a leadframe) that provides electrical connections from the die to the exterior of the package carrier. In one such packaging arrangement called flip chip mounting, the die includes an array of electrically conductive contacts, known as bonding pads, that may electrically connected by solder balls or bumps to a corresponding array of bond pads on a substrate, such as a package carrier. Typically, the solder bumps are registered with the bond pads on the die and/or substrate and reflow processes are applied to create electrical connections in the form of solder joints between the die and the substrate. The process of flip chip mounting results in a space or gap between the die and the substrate.
In many of these conventional processes, aluminum or gold has been used for forming the bond pads. However, copper is currently more prevalent because of the costs associated with gold and because copper is a better conductor than aluminum. Still, the use of copper has not been without difficulty because copper readily oxidizes at standard temperature and pressures. Areas of oxidized copper greatly reduce the reliability of the electrical connection by disrupting current flow.
Thus, there remains a need for fabrication methods that improve the reliability of electrical connections made with copper surfaces in semiconductor devices.